In general, flexible pipes used for piping in airplanes, vehicles, mechanical facilities, and buildings are formed of stainless steel and connecting structures, such as flanges or elbows, are connected at both ends thereof by an arc welding method, a plasma welding method, a brazing welding method, or by using screw connecting structures.
A stainless flexible pipe has a thickness of 0.3 mm or less and a nipple or fitting of a connecting structure welded thereto generally has a thickness of 1 mm or more. Due to a difference in thickness, thin plate welding was impossible.
Accordingly, a ring for welding with a thickness of 0.5 mm or more was first welded to the flexible pipe by arc welding or plasma welding, and then the ring for welding was welded to the nipple or fitting of the connecting structure. This required a complicated welding process and high welding costs. Moreover, cracks or corrosion occurred at thin welded bead zones and heat affected zones of the flexible pipe due to a welding stress.
Meanwhile, a brazing welding method could not be performed by a less skilled welding operator but only by a person skilled in the welding art in the case of welding a short-length flexible pipe to a connecting structure having a nipple or fitting with a thickness of 1 mm or more. Further, there was a problem in that cracks and corrosion took place at welded zones and heat affected zones due to a welding stress.